The invention relates to field programmable gate array circuits used in digital circuit design, and in particular, to a simplified architectural design for their implementation on a molecular level related to U.S. Pat. No. 6,215,327.
A detailed background for the present invention can be found in U.S. Pat. No. 6,215,327, entitled Molecular Field Programmable Gate Array, which is hereby incorporated by reference in its entirety. The key concept introduced in '327 is that by connecting together a feed-forward network of identical, elemental assemblies referred to as look-up tables or LUTs, it is possible to form a field programmable gate array (FPGA) capable of computing any spatial Boolean function so long as the array is sufficiently large. The novelty of the molecular field programmable gate array lies in its ability for complex expression by using simple building blocks with low interconnection demand (only nearest-neighbor connectivity is required) that are arranged in a completely periodic fashion.
It is believed that three requirements for molecular electronics are: (1) low interconnection demand, (2) defect tolerance, and (3) capable of manufacture through non-lithographic methods. In traditional integrated circuits built in silicon, these boundary conditions are desirable but not essential. Low interconnection demand, for example, is compensated for by having many levels of planar interconnections (i.e., increased interconnection supply). In traditional microelectronics, defect tolerance is removed as a requirement by having fabrication processes that achieve very low numbers of defects, such that the production of integrated circuits has a high enough yield to be economically tractable. Finally, the cornerstone of conventional integrated circuits is lithography, and it is inconceivable to the present industry to attempt to construct complex circuits without it. This is because, most fundamentally, it is lithography which defines deliberate and complex patterns of the diffusion zones that become transistors and the interconnection patterns that bring them together to form complex digital circuits. However, this plan does not work at molecular scales, since high-volume lithography is impossible, as we presently understand technology. Furthermore, the sheer density of molecular circuits compromises the notion of high availability of interconnections. Finally, it is envisioned that defect mechanisms will be abundant. Even if lithography and interconnection supply were not issues, the likely pervasiveness of defects would render most normal integrated circuit designs inoperative.
U.S. Pat. No. 6,215,327 identified an alternative scheme. Its fundamental requirement was the existence of a simple, programmable cell, which upon arranging a number of them into a planar or 3-D array, could yield complex behaviors. In fact, the invention was the basis of perhaps the simplest conceivable FPGA, which could be harnessed to implement very complex circuits by programming each site as required after assembly so that the ensemble produced a desired set of circuit functions.
In the '327 patent, a number of templates were defined, each of which required cells or sites with a minimum of three inputs or three outputs. Every concept of that invention applies to the present invention, except that two newer and simpler templates, specifically templates requiring only two inputs and two outputs, are now introduced.